Periodic Reporting for period 4 - TEMPO (Terrestrial vertebrates and the evolutionary origins of morphological diversity)
Berichtszeitraum: 2020-11-01 bis 2021-10-31
The approach of the project is to address three central questions:
(1) How have rates and constraints of phenotypic evolution varied through geological time? This is a quantitative statistical question. By quantifying the structure of the skeleton in many species, including both living and fossil animals, we hope to characterise how patterns of evolution vary among groups and through time. Understanding *how* they vary is the first step in answering *why* they vary.
(2) Are these patterns consistent with the occurrence of global niche-filling? This relates to the hypothesis of adaptive radiations, that evolution of organisms is a response to the distribution of ecological opportunities on Earth through time.
(3) Can evolutionary versatility enabled by key innovations explain these patterns? This relates to the hypothesis that some groups of animals are simply more versatile than others, due to features of their body plan, structure, or development.
We also addressed questions of ecomorphology and evolution within groups such as marsupials, birds and dinosaurs. Ecomorphology is the study of relationships between the structure of organisms and their ecology. It is central to core macroevolutionary hypotheses such as the idea of adaptive radiation (that evolution is driven by availabilities of novel ecological opportunities) and also to interpreting the ecologies of extinct species known only from fossils (including dinosaurs). Among other findings made so far, the quantitative approaches of the project have uncovered new indicators of stance in extinct animals, allowing us to determine which dinosaurs were quadrupeds, and which were bipeds. We have also investigated links between the vestibule (organ of balance) in birds and their locomotion, found clear skeletal evidence that distinguishes between nocturnal and diurnal animals, or swimming and non-swimming animals. These have been used to investigate the ecologies of extinct species including dinosaurs (https://www.nature.com/articles/s41586-022-04528-0
The major work of the project involved using quantitative data to understand importance of variation in evolutionary constraints for major patterns of disparity (variation in morphological diversity among groups and through time). To this end, we developed new statistical approaches to quantify this variation using both discrete anatomical observations (in character-taxon matrices), and using geometric morphometric data that summarise the structure of the whole skeleton. Much of this work is published or in review and includes evidence that the early Cenozoic mammal radiation was initially highly constrained (https://www.sciencedirect.com/science/article/abs/pii/S0960982221005911) as well as large differences in patterns of morphological evolution between the early ancestors of mammals, compare to early reptiles (https://academic.oup.com/sysbio/advance-article/doi/10.1093/sysbio/syac020/6547063). Morphometric studies of birds are published or in review, highlighting patterns of variation in ecological signal across the bird skeleton (https://www.nature.com/articles/s41559-021-01509-w.epdf) and uncovering large differences in the mode of skeletal evolution among bird groups and through time that shaped their living diversity. These studies are highly innovative becuase they use data from across the whole skeleont, or most of it. This differs from previous studies that focussed just on partsof the animal such as the skull or beak, yielding a very incomplete view of evolution. A major outcome of the project is to have such data for birds and also mammals, and analysis of mammal data is ongoing, revealing large differences in how skeletal evolution proceeds in mammals compared to birds.
Project results have been disseminated through scientific publications and media release, and also through conference presentations.
By the end of the project we expect to have synthesised and compared patterns of skeletal evolution from across birds, mammals, and their extinct relatives (dinosaurs mammal-like reptiles, and others). By doing so we hope to understand how patterns of the rate of evolution, and constraints on its outcomes, vary among groups and through time. This will shed light on the factors (e.g. evolutionary versatility, ecological opportunity) underlying the large-scale patterns of evolutionary history.